A New Data Link Layer Protocolfor Satellite IP Networks

1. Niraj Solanki

2. The satellite network :-
1. Wider coverage and broadcasting capabilities.
2. independent for distance.
3. point-to-multipoint broadcasting services.
4. suitable for providing multimedia applications and Internet services for
both fixed and mobile users.
Due to the long time delay, the high data error, the low bandwidth
utilization and the high cost of communication, service integration
capabilities defects and is poor which lead satellite networks difficult to
meet the user cheap and convenient services.

3. In the TCP/IP protocol suite, the purpose of the data link layer is to send and
receive
(1) IP datagram for the IP module
(2) ARP requests and replies for the ARP module.
Currently, in the satellite networks, the application protocol of data link layer is
less, and there are two kinds mainly application protocols:
CCSDS protocol and HDLC protocol.
CCSDS:- Consultative Committee for Space Data System.

4. CCSDS:- Consultative Communication for Space Data System.
HDLC:- High Level Data Link Control.
FCS:- Frame Check Sequence.

5. Satellite network's features :-
[A] The features and influence of the satellite network :-
1. The satellite's large coverage area and multi-beams
 Distance from the satellite to the Earth's surface : more than 1000 of km.
 The satellite‘s coverage area will be very great.
 Geostationary satellite can cover one third of the Earth's surface.
MEO satellite whose orbital altitude is 5000 km, pitch angle is 1.5 degrees
and each satellite beam's coverage area is approximately 54000 square
kilometers.

6. This features will produce the following effects in the data frame transmission
and switching :-
Using of the address in link layer data frame to achieve the switching will be
very difficult when different terrestrial networks within the same beam for data
transmission and switching because of the different network address
Only using of the address in data link layer data frame to achieve the switching
will also be very difficult when the terrestrial networks belongs to different
beams for data transmission and switching because the network address is
different.
Only using the data link layer protocol will be unable to achieve when the
terrestrial networks belongs among different satellites for data transmission
and switching, as which require routing and switching between the satellites.

7. The satellite's high speed movement and frequently changing network topology
Satellite earth links between satellite network and terrestrial network change
quickly because a satellite‘s coverage area changes frequently;
if only using data link layer protocol to achieve data transmission and switching
of the satellite network may result in loss of packet data and not guarantee the
transmission quality because of the changes in satellite earth links and inter-
satellite links.
Physical limitation of the satellite system and the limited information
transmission bandwidth
Data processing capability of the satellite network is low and the information
transmission bandwidth is limited when compared with the terrestrial network
as the satellite energy, computing resources, storage resources are very
limited. What requires that minimize the overhead of the
transmission data and improve the utilization of transmit information.

8. Introduction of the NSLP protocol
NSLP (New Satellite Link Protocol)
the frame format
1. SFD ( Start of Frame Delimiter)--(1 byte, 10101011).
2. SFD is added by the physical layer, belongs to the physical layer header,
serve as a start flag of the data frame and represent a new data frame.
3. The last two bits are "11", which indicates the next numeric field is the
contents of the data frame.

9. Data-- it is data which encapsulated by the upper layer protocol.
CRC--2bytes, CRC are used to achieve error detection of the frame data.
The structure of the NSLP protocol is simple and the function of each
numeric fields are effectively applied in actual use.
In this protocol, the data link layer is only responsible for data's frame
encapsulation, transmission and the necessary error detection, no longer
responsible for addressing and switching of the data frame.

10. SIMULATION RESULTS AND PERFORMANCE
ANALYSIS
1) Comparison of Information Transmission Efficiency: -
comparing different protocols from 64 bytes to 1500 bytes.
Figure shows the cost of these four kinds of protocol's data frame header.
the information transfer efficiency,
NSLP protocol is the highest, which
is followed by the HDLC protocol,
next one is the CCSDS protocol,
and IEEE802.3 protocol's efficiency
is the lowest.

11. b) Information transfer efficiency of fixed length IP packet transmission
Table 1 shows that when the length of IP packet data are 64 bytes, NSLP
protocol message transmission efficiency is increased by 3.03%, 5.59%,
7.09% respectively, compared to HDLC, CC SDS, 802.3 protocol When the
IP packet data length is greater than 512 bytes, then the transmission
efficiency is improved closely to 1%.
NSLP protocol reduces the cost of link layer datagram header and improves
the efficiency of information transmission.

12. 2) Comparison of loss rate of IP packet
According to the number of IP packet encapsulation, four protocols can be
divided into two categories:-
Fixed length frame Variable length frame
The former one includes CCSDS, while the latter one includes NSLP,
HDLC, and IEEES02.3 frame . To compare the loss rate of NSLP protocol, the
following two situations are proposed.
a) Loss rate of an IP packet in variable length frame
• assume the IP packet length is X bytes,
• the data frame length is Y bytes,
• information transmission error rate is represented by Pe .
• Since each variable length frame is encapsulated into one IP packet, the
IP packet loss rate is:
γ
e )P(P  111

13. b) Loss rate of IP packet infixed-length frame
1. Assume IP packet length is X bytes, the data frame length of Y bytes.
2. The information transmission error rate Pe, and M (number of IP packets) is
just encapsulated exactly into N (number of data frames) completely.
3. denote that T= [M/ NJ , then each IP packet is encapsulated into T split or
T+1 data frame.
4. At this time, if any one of the data frames has problems, will lead to errors of
the IP packet, and cause it be discarded eventually.
5. The calculation on loss rate of IP packet with fixed-length frames is:

15. B) Performance Analysis:-
1) Good compatibility with TCP/IP protocol :-
CCSDS protocol is a data link layer protocol among SCPS protocol suite.
However, SCPS protocol changes in many ways from the transport layer to the
data link layer, without considering the compatibility with TCP/IP protocol.
HDLC protocol is then a data link layer protocol that is designed specifically for
OSI protocol architecture by ISO organization. Therefore, both the two
protocols show bad compatibility with TCP/IP protocol.
Based on TCP/IP protocol, NSLP protocol is also a data link protocol proposed
for the satellite IP network. For the reason that it does not modify the protocol
of transport layer and network layer, the compatibility with TCP/IP protocols is
guaranteed very well.
SCPS:- Space Communication Protocol Suite.

16. 2) High coupling degree with IP protocol:-
CCSDS data frame is a fixed length frames. When encapsulating the data
frame, few IP packets will be packed into a data frame. Also there is a situation
that the data will be decomposed into two data frames, from one IP packet.
On transfer process, once a data frame comes to an error, not only the whole
IP packets in current data frame will be discarded, but also cause a problem
that other IP packet data frame can't be resolved. Thus error propagation
occurs.
The NSLP data frame is a data frame with variable length. Its length is closely
in correlation with encapsulated IP packet data.
When transmitting the data frame, if a error occurs to a IP datagram, only
current data frame needs to be discarded, which does not affect the other IP
packet data's transmission. Therefore, NSLP protocol has a high coupling
degree with IP protocol.

17. CONCLUSION
We demonstrate that the protocol simplifies the function and streamlines data
frame format. Besides, this protocol has a list of advantages. They are high
transmission efficiency, low IP packet loss rate, good compatibility with the
TCP/IP protocol, high degree of coupling with IP protocol, and great savings
onboard resources. In the process of the information transmission and
exchange, it is also good for the entire satellite IP networks, indeed improving
the performance. Also, this paper laid the foundation for further in-depth study of
new satellite IP network routing strategy.

18. Reference:-
“A New Data Link Layer Protocol for Satellite IP Networks”, Liu Jiong, Chen
Guang, Zhang Jingbin, Sun Pengchun, 2013 International Conference on
Mechatronic Sciences, Electric Engineering and Computer (MEC), Dec 20-22,
20l3, Shenyang, China