Giao thức HDLC

[Guest]

Em muốn hỏi giao thức HDLC là gì?
Cấu trúc khung trong giao thức HDLC là như thế nào ?
Hoạt động của giao thức này là như thế nào?
Em nhận được bài tập lớn là nối hai máy tính bằng giao thức HDLC?
Trong đó phần cứng là 2 bộ HDLC controller làm nhiệm vụ tạo frame , bit stuffing....
Và phần mềm điều khiển , kiểm soát quá trình truyền dữ liệu giữa hai máy .
Em muốn hỏi phần mềm này thì nên viết bằng ngốn ngữ gì ?
Ai có sơ đồ mạch con HDLC controller thì cho em xin với ?
Rất mong nhận được câu trả lời !

[tranmyphuc]

Em muốn hỏi giao thức HDLC là gì?
Cấu trúc khung trong giao thức HDLC là như thế nào ?
Hoạt động của giao thức này là như thế nào?
Em nhận được bài tập lớn là nối hai máy tính bằng giao thức HDLC?
Trong đó phần cứng là 2 bộ HDLC controller làm nhiệm vụ tạo frame , bit stuffing....
Và phần mềm điều khiển , kiểm soát quá trình truyền dữ liệu giữa hai máy .
Em muốn hỏi phần mềm này thì nên viết bằng ngốn ngữ gì ?
Ai có sơ đồ mạch con HDLC controller thì cho em xin với ?
Rất mong nhận được câu trả lời !

HDLC Protocol Description

HDLC [High-level Data Link Control] is a group of protocols for transmitting [synchronous] data [Packets] between [Point-to-Point] nodes. In HDLC, data is organized into a frame. HDLC protocol resides with Layer 2 of the OSI model, the data link layer.
HDLC uses zero insertion/deletion process [bit stuffing] to ensure that the bit pattern of the delimiter flag does not occur in the fields between flags. The HDLC frame is synchronous and therefore relies on the physical layer to provide method of clocking and synchronizing the transmission and reception of frames.




General HDLC Frame

Opening Flag, 8 bits [01111110], [7E hex]
Address, 8 bits [ could be more]
Control, 8 bits, or 16 bits
Data [Payload], Variable, not used in some frames, or may be padded to complete the fill
CRC, 16 bits, or 32 bits
Closing Flag, 8 bits [01111110], [7E hex]

User data which contains 7E is resolved using an escape sequence which converts 7E to 7D-5E [with 7D being the escape character]. If 7D is used in the data stream it again is converted into 7D-5D. Address 11111111 is known as all stations, 00000000 is this station.

Frames may be aborted by sending an abort sequence [01111111] instead of the normal flag sequence [01111110]. An abort sequence will cause the frame to be discarded. During idle times when no frames are being transmitted idle flags [11111111] may be sent to fill the area between frames. A continuous series of flags [01111110] may be sent to fill the area between frames instead of sending idle flags [11111111].

Fill between Frames

HDLC Opening Flag
8 bits [01111110], [7E hex]
The Opening flag may be preceded by additional flags [01111110] or idle flags [11111111], both used as inter-frame fill.



HDLC Address Field
HDLC Address Field
The length of the address field depends on the data link layer protocol used, but is normally 0, 8 or 16 bits in length. In many cases the address field is typically just a single byte, but an Extended Address [EA] bit may be used allowing for multi-byte addresses. A one residing in the LSB bit indicates [the end of the field] that the length of the address field will be 8 bits long. A zero in this bit location [now the first byte of a multi-byte field] indicates the continuation of the field [adding 8 additional bits]. The SDLC protocol will use only an 8 bit address. The SS7 protocol, which is used in point-to-point links, does not use an address field at all.

The first [MSB] bit in the Address field indicates if the frame is a unicast or multi-cast message. A zero in the MSB bit location indicates a unicast message; the remaining bits indicate the destination node address. A one in the MSB bit location indicates multicast message, the remaining bits indicate the group address.


HDLC Control Field
The Control field is 8 or 16 bits and defines the frame type; Control or Data. The Control field is protocol dependent.

HDLC Data Field
The Data field may vary in length depending upon the protocol using the frame. Layer 3 frames are carried in the data field.

HDLC FCS Field
FCS [16 bits] = X16 + X12 + X5 + 1
FCS [32 bits] = X32 + X26 + X23 + X22 + X16 + X12 + X11 + X10 + X8 + X7 + X5 + X4 + X2 + X + 1
Frame Encapsulation:
A few different versions of the HDLC frame are shown below. These include the PPP [Point-to-Point Protocol] HDLC frame, and the Ethernet HDLC frame.

Ethernet HDLC Frame Encapsulation

Ethernet Frame Encapsulation:
The Preamble [a specific bit pattern] Informs the receiving station that a new packet is arriving and synchronizes the receive clock with the transmitted clock. Used in Ethernet, not HDLC.

The Address Field consists of a Source Address and/or a Destination Address. The Source and Destination Addresses identify the sender [Source] and receiver [Destination]. The Source Address is used to identify to the network that's sending data. The Destination Address is used to identify who should be receiving the data. Some protocols may only have one address.

The Control Field indicates the type of Information that is being sent as Data. It identifies the purpose of the packet as Data or Control information, and may also indicate the size of the packet and Data.

The Data Field is the actual information being transmitted. It can contain Control Information for handshaking, or actual Data used by applications.

The CRC [Cyclic Redundancy Checking] or FCS [Frame Check Sequence] contains an error checking number that the Destination can use to verify that the packet is error free.

The End Frame Delimiter has a specific bit pattern. This bit pattern identifies the end of the packet to the Destination. Protocols with fixed packet size may not require an End Frame Delimiter.

For some physical interfaces [SDH or SONET] after the data as been encapsulated into the frame it must still be scrambled before being sent to the physical layer [from the Link layer].



Point-to-Point Protocol HDLC Frame Encapsulation

Point-to-Point Protocol Frame Encapsulation:
Point-to-Point Protocol [PPP] is used in transporting multi-protocol datagrams over point-to-point links. PPP is capable of operating on many DTE/DCE interfaces (such as, RS-232C, RS-422, RS-423 or V.35). PPP is used with full-duplex circuits [dedicated or circuit-switched] operating in either an asynchronous (start/stop), bit-synchronous, or octet-synchronous mode, transparent to PPP Data Link Layer frames. PPP does not require the use of control signals, such as Request To Send (RTS), Clear To Send (CTS), Data Carrier Detect (DCD), and Data Terminal Ready (DTR). For asynchronous links, inter-octet and inter-frame time fill MUST be accomplished by transmitting continuous "1" bits.

HDLC IC Manufacturers

HDLC: High-Level Data Link Control.
SDLC: Synchronous Data Link Control. Link layer protocol based on synchronous, bit-oriented operation. Other Protocols; LAP; Link Access Procedure and LAPB; Link Access Procedure, Balanced, PPP Point-to-Point Protocol and Frame Relay.
HDLC Standards and Specifications

[IS 3309]: Information Processing Systems--Data Communication High-Level Data Link Control Procedure--Frame Structure

From : http://www.interfacebus.com/Design_HDLC.html

Hoặc tải slide tóm tắt những cái bạn cần ở đây : http://www.cse.hcmut.edu.vn/~bvhieu/..._Data_link.pdf

Chúc bạn vui !!!

[dt3_27]

cảm ơn bác Phúc . Em muốn hỏi muốn lập hỏi lập trình thì mình nên dùng ngôn ngữ nàolà mạnh nhất ? C có được không?

[tranmyphuc]

cảm ơn bác Phúc . Em muốn hỏi muốn lập hỏi lập trình thì mình nên dùng ngôn ngữ nàolà mạnh nhất ? C có được không?

Theo mình thì có thể dùng C hoặc C++
Bạn tham khảo một phần mềm simulation tại đây :

http://www.tek.com/Measurement/cgi-bin/framed.pl?Document=/Measurement/Products/catalog/k1197/sw/psisdn/&FrameSet=communications

Chúc bạn vui !!!

[dt3_27]

nhờ các bác xem giúp con CX28500 có phải là con HDLC controller không nhé
giá nó bao nhiêu
Mua ở đâu thế

[hole]

bạn ơi bạn nói cụ thể về trường address của HDLC hơn nữa được hok?

[vnpro-test]

bạn ơi bạn nói cụ thể về trường address của HDLC hơn nữa được hok?

In broadcast and multicast frames, the most significant bit of the
HDLC address must be 1 [1]. In addition, the least significant bit
must always be 1 to indicate the end of the field [1].

In the case of IP broadcast, the remaining six bits of the HDLC
address must be all 1s. That is, it should be mapped to the HDLC
broadcast address 0xFF (hexadecimal).

In the case of IP multicast, the remaining six bits of the HDLC
address must contain the lowest-order six bits of the IP multicast
group address. It resembles IP multicast extension for ethernet
described in [9]. Exceptions arise when these six bits are either
all zeros or all ones, in which case they should be altered to the

bit sequence 111110.

Có thể xem thêm trong
RFC 2176 và RFC 1662

[popbob]

cho mình hỏi muốn thiết kế HDLC thì mình cần dùng IC nào, và ở Hà nội hoặc TP HCM thì có bán loại IC đó không

[hoanggialiem]

Một số loại IC:

Zilog - HDLC chip, MCU with HDLC
Samsung - MCU(S3C4510 - Arm7) with HDLC
Hitachi - HDLC chip
Infineon - HDLC chip, MCU(C165 UTAH, C165 H) with HDLC
Samsung - MCU(Arm7) with HDLC
AMD - MCU(Am186cc) with HDLC
Motorola - MCU(MC68302 & MPC860 & MPC8260) with HDLC
Rabbit - MCU(R3000) with HDLC
Mindspeed - HDLC chip
infinior - MCU(ims16c - x86 compatible) with HDLC www.infinior.com

Z85C30 & Z85230 - It's popular & best.

Samsung S3C4510 - It's good & cheap.

MPC8260 - It's High-performance & expensive.

Mình thấy HN có cửa hàng này cũng đa dạng SP: http://www.icvn.com.vn