Shulou(Shulou.com)05/31 Report--

This article introduces what are the knowledge points of E1 line, the content is very detailed, interested friends can refer to, hope to be helpful to you.

E1 line knowledge point

1. E1 is a 2.048m link, which is encoded by PCM.

2. The frame length of an E1 is 256bit, which is divided into 32 time slots, and one time slot is 8 bit.

3. Every second, 8k frames of E1 pass through the interface, namely 8K*256=2048kbps.

4. Each time slot accounts for 8 bits in E1 frame, that is, 32 64K in an E1 frame.

E1 frame structure

E1 has three ways: framing, complex framing and non-framing. In framed E1, the 0th time slot is used to transmit frame synchronization data, and the remaining 31 time slots can be used to transmit valid data. In framed E1, except for the zero time slot, the 16th time slot is used for signaling, and only 30 time slots from 1 to 15, 17 to 31 can be used to transmit valid data. In the unframed E 1, all 32 time slots can be used to transmit valid data.

I. basic knowledge of E1

A brief introduction to the frame structure of E1 Channel

In E1 channel, 8bit forms a time slot (TS), 32 time slots constitute a frame (F), and 16 frames form a complex frame (MF). In one frame, TS0 is mainly used to transmit frame positioning signal (FAS), CRC-4 (cyclic redundancy check) and peer alarm indication, while TS16 mainly transmits signaling with channel (CAS), multiple frame location signal and complex frame opposite end alarm indication, and transmits voice or data in 30 time slots from TS1 to TS15 and TS17 to TS31. We call TS1 to TS15 and TS17 to TS31 as "payloads" and TS0 and TS16 as "expenses". If out-of-band common channel signaling (CCS) is used, TS16 loses the use of transmitting signaling, and the time slot can also be used to transmit information signals. In this case, the payload of the frame structure is TS1 to TS31, and the overhead is only TS0.

Introduced by PCM coding E1:

According to the slot characteristics of E1 in PCM coding, E1 is divided into 32 time slots TS0-TS31. Each time slot is 64K, in which TS0 is occupied by frame synchronization code, Si, Sa4, Sa5, Sa6,Sa7,A bits. If the system uses CRC check, the Si bit position transmits CRC check code. TS16 is a signaling slot, which is used to transmit signaling when signaling (co-channel signaling or follower signaling) is used. Users cannot use it to transmit data. So the PCM code type of 2m has

① PCM30: 30 available time slots for PCM30 users, TS1-TS15

TS17-TS31 . TS16 transmits signaling without CRC check.

② PCM31: 31 available time slots for PCM30 users, TS1-TS15

TS16-TS31 . TS16 does not transmit signaling and has no CRC check.

③ PCM30C: 30 available time slots for PCM30 users, TS1-TS15

TS17-TS31 . TS16 transmits signaling with CRC check.

④ PCM31C: 31 available time slots for PCM30 users, TS1-TS15

TS16-TS31 . TS16 does not transmit signaling and has CRC check.

CE1, which divides the 2m transmission into 30 64K time slots, is generally written as Number64.

You can use several of these slots, that is, only n 64K, which must be connected to the ce1/pri.

CE1---- can have up to 31 channels to carry data timeslots 1 Murray Murray 31

Timeslots 0 transmission synchronization

II. Interface

G.703 unbalanced 75 ohm, balanced 120 ohm2 interfaces, interchangeable

Three. There are three ways to use E1

1, using the entire 2m as a link, such as DDN 2m

2, use 2m as several 64k and their combinations, such as 128Kpr 256k, etc., this is CE1

3. When used as a digital relay for voice exchange, this is also the most original use of E1. It uses an E1 as 32 64K, but slot 0 and slot 15 are used as signaling signaling, so an E1 can transmit 30 voice. PRI is one of the most commonly used access methods, and the standard is called PRA signaling.

Use the wide area network interface card of 2611 and connect the E1 line through V.35-G.703 converter. Such a cost should be lower than the E1 card, the current DDN 2 M rate line is usually pulled to the subscriber side via the HDSL line.

E 1 can be pulled from the optical fiber from the transmission equipment to the optical terminal on the user side to provide E 1 service.

Four. points for attention in use

When the E1 interface is docked, there must be no signal loss / frame out-of-step / multi-frame out-of-step / slip code alarm on the E1 interface, but the two sides must be exactly the same on the E1 interface parameters because of the inconsistency of individual characteristic parameters. There will not be any alarm on the indicator or alarm station, but it will cause data channel failure / error code / slip code / out-of-step and so on. These characteristic parameters are mainly: impedance / frame structure / CRC4 check, there are two kinds of 75ohm and 120ohm, and there are three kinds of frame structure: PCM31/PCM30/ is not framed; in the Xinqiao node machine, PCM31 and PCM30 are described as CCS and CAS respectively, and when docking, the network administrator should be told to choose CCS, whether or not to carry out CRC check can be flexibly chosen, the key is to be consistent between both sides, so that the normal physical layer can be ensured.

5. Question

1. Who controls E1 and CE1, telecom or user equipment on both sides of the interconnection? The user side must ask to support them, and how does the telecom realize it separately?

First of all, it is decided by Telecom that Telecom can provide E1 and CE1 lines, but the E1 lines of general users are all CE1, unless you especially want to use E1 only, and then it is determined by your equipment. CE1 can be used as E1, but E1 cannot be used as CE1.

2. CE1 is available for 32 time slots, right?

The 0 and 16:00 slots of CE1 are not used. 0 is to transmit the synchronization number, and 16 to transmit control commands. Only 30 time slots 1-15 min 16-30 can actually be used.

3. How does E1/CE1/PRI distinguish the relationship between 2m and 2m? How does it relate to the 2m of DDN?

Both E1 and CE1 are E1 line standards, PRI is the ISDN trunk line, and the 2m of 30BDC DDN is a transparent line. you can run any protocol on it. Of course, the difference between E1 and CE1 can be divided into time slots.

4. What is the relationship between E1/CE1/PRI and signaling and time slot?

E1CE1 is 32 slots, 30 slots, 0 and 16 respectively to transmit synchronous signal and control signal. PRI uses 30B+D, 30B to transmit data, D channel to transmit signaling, E1 is CAS structure, which is called in-band signaling, PRI signaling and data transmission separately, namely out-of-band signaling.

5. Can CE1 connect E1?

CE1 and E1 can of course be interconnected. But CE1 must be used as E1, that is, it can not be divided into time slots.

6. In order to realize one-to-multipoint interconnection using CE1, the center must be 2m and the branch rate is 64K.

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